1. Field of the Invention
The present invention relates to a process for preparing a polymer-modified pigment comprising the step of: combining, in any order, a pigment having attached at least one nucleophilic group, a polymer comprising at least one carboxylic acid group or salt thereof, and a coupling agent.
2. Description of the Related Art
The surface of pigments contain a variety of different functional groups, and the types of groups present depend on the specific class of pigment. Several methods have been developed for grafting materials and, in particular, polymers to the surface of these pigments. For example, it has been shown that polymers can be attached to carbon blacks containing surface groups such as phenols and carboxyl groups. However, methods which rely on the inherent functionality of a pigment's surface cannot be applied generally because not all pigments have the same specific functional groups.
Methods for the preparation of modified pigment products have also been developed which can provide a pigment with a variety of different attached functional groups. For example, U.S. Pat. No. 5,851,280 discloses methods for the attachment of organic groups onto pigments including, for example, attachment via a diazonium reaction wherein the organic group is part of the diazonium salt.
Other methods to prepare modified pigments have also been described. For example, PCT Publication No. WO 01/51566 discloses methods of making a modified pigment by reacting a first chemical group and a second chemical group to form a pigment having attached a third chemical group. Ink compositions containing these pigments are also described.
While these methods provide modified pigments having attached groups, there remains a need for improved processes for attaching groups and, in particular, polymeric groups, to a pigment. These additional methods may provide advantageous alternatives to forming modified pigments.